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Chapter 20 Communities and Ecosystems PowerPoint® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc. Biology and Society: Does Biodiversity Matter? • The expanding human population threatens – Biodiversity – The loss of natural ecosystems • Biological diversity, or biodiversity, includes – Genetic diversity – Species diversity – Ecosystem diversity © 2010 Pearson Education, Inc. Figure 20.00 • Healthy ecosystems – Purify air and water – Decompose wastes – Recycle nutrients • Wetlands – Buffer coastal populations against hurricanes – Reduce the impact of flooding rivers – Filter pollutants • It is estimated that the average annual value of ecosystem services each year in the United States is more than $33 trillion. © 2010 Pearson Education, Inc. Genetic Diversity • The genetic diversity within populations of a species is the raw material that makes microevolution and adaptation to the environment possible. • Genetic resources for that species are lost if – Local populations are lost – The number of individuals in a species declines • The present rate of species loss – May be 1,000 times higher than at any time in the past 100,000 years – May result in the loss of half of all living plant and animal species by the end of this century © 2010 Pearson Education, Inc. Figure 20.1 • Two recent victims of human-caused extinctions are – Chinese river dolphins – Golden toads © 2010 Pearson Education, Inc. Ecosystem Diversity • The local extinction of one species can have a negative effect on the entire ecosystem. • The loss of ecosystems risks the loss of ecosystem services, including – Air and water purification – Climate regulation – Erosion control © 2010 Pearson Education, Inc. • Coral reefs are rich in species diversity, yet – An estimated 20% of the world’s coral reefs have been destroyed by human activities – 24% are in imminent danger of collapse – Another 26% of coral reefs may succumb in the next few decades if they are not protected © 2010 Pearson Education, Inc. Figure 20.3 Causes of Declining Biodiversity • Ecologists have identified four main factors responsible for the loss of biodiversity: 1. Habitat destruction and fragmentation 2. Invasive species 3. Overexploitation 4. Pollution © 2010 Pearson Education, Inc. Habitat Destruction • Biodiversity is threatened by the destruction and fragmentation of habitats by – Agriculture – Urban development – Forestry – Mining © 2010 Pearson Education, Inc. Figure 20.4 Figure 20.5 Pollution • Acid precipitation is a threat to Forest ecosystems and Aquatic ecosystems • Aquatic ecosystems are polluted by toxic chemicals and nutrients © 2010 Pearson Education, Inc. Interspecific Interactions • An organism’s biotic environment includes – Other individuals in its own population – Populations of other species living in the same area • Interspecific interactions are interactions between species. © 2010 Pearson Education, Inc. Figure 20.6 • Interspecific interactions can be classified according to the effect on the populations concerned. – –/– interactions occur when two populations in a community compete for a common resource. – +/+ interactions are mutually beneficial, such as between plants and their pollinators. – +/– interactions occur when one population benefits and the other is harmed, such as in predation. • In interspecific (between species) competition, the population growth of a species may be limited by – The population densities of competing species – By the density of its own population © 2010 Pearson Education, Inc. • An ecological niche is the sum of an organism’s abiotic and biotic resources in its environment. • The competitive exclusion principle states that if two species have an ecological niche that is too similar, the two species cannot coexist in the same place. © 2010 Pearson Education, Inc. (a) Virginia’s warbler (b) Orange-crowned warbler Figure 20.7 LM Relative population density Separate cultures Paramecium aurelia Combined cultures 2 P. aurelia 4 6 8 10 Days 12 14 16 LM 0 P. caudatum Paramecium caudatum Figure 20.8 Mutualism (+/+) • In mutualism, both species benefit from an interaction. • One example is the mutualistic relationship of coral animals and the unicellular algae that live inside their cells. – The coral gains energy from the sugars produced by the algae. – The algae gain – A secure shelter – Access to light – Carbon dioxide – Ammonia, a valuable source of nitrogen © 2010 Pearson Education, Inc. Figure 20.9 Predation (+/–) • Predation refers to an interaction in which one species (the predator) kills and eats another (the prey). • Numerous adaptations for predator avoidance have evolved in prey populations through natural selection. • Cryptic coloration is – Camouflage – A way for prey to hide from predators • A warning coloration is a – Brightly colored pattern – Way to warn predators that an animal has an effective chemical defense © 2010 Pearson Education, Inc. Figure 20.10 Figure 20.11 • Mimicry is a form of defense in which one animal looks like another species. © 2010 Pearson Education, Inc. Herbivory (+/–) • Herbivory is the consumption of plant parts or algae by an animal. • Plants have evolved numerous defenses against herbivory, including – Spines – Thorns – Chemical toxins © 2010 Pearson Education, Inc. Parasites and Pathogens (+/–) • Plants and animals can be victims of – Parasites, an animal that lives in or on a host from which it obtains nutrients – Pathogens, disease-causing – Bacteria – Viruses – Fungi – Protists © 2010 Pearson Education, Inc. Trophic Structure • Trophic structure is the feeding relationships among the various species in a community. • A community’s trophic structure determines the passage of energy and nutrients from plants and other photosynthetic organisms – To herbivores – And then to predators • The trophic level that supports all other trophic levels consists of autotrophs, also called producers. © 2010 Pearson Education, Inc. • All organisms in trophic levels above the producers are heterotrophs, or consumers. • Primary consumers are called herbivores, which eat plants. • Above the level of primary consumers are carnivores, which eat the consumers from the level below. – Secondary consumers eat primary consumers. – Tertiary consumers eat secondary consumers. – Quaternary consumers eat tertiary consumers. © 2010 Pearson Education, Inc. Quaternary consumers Carnivore Carnivore Tertiary consumers Carnivore Carnivore Secondary consumers Carnivore Carnivore Primary consumers Zooplankton Herbivore Producers Plant A terrestrial food chain Phytoplankton An aquatic food chain Figure 20.15-5 • Detritivores, which are often called scavengers, consume detritus, the dead material left by all trophic levels. • Decomposers are prokaryotes and fungi, which secrete enzymes that digest molecules in organic material and convert them into inorganic forms. © 2010 Pearson Education, Inc. Figure 20.16 Biological Magnification • Environmental toxins accumulate in consumers at higher concentrations up a trophic system in a process called biological magnification. © 2010 Pearson Education, Inc. Increasing concentrations of PCBs Herring gull eggs 124 ppm Lake trout 4.83 ppm Smelt 1.04 ppm Zooplankton 0.123 ppm Phytoplankton 0.025 ppm Figure 20.17 Food Webs • Few ecosystems are as simple as an unbranched food chain. • Omnivores – Eat producers and consumers – Form woven ecosystems called food webs © 2010 Pearson Education, Inc. Quaternary, tertiary, and secondary consumers Tertiary and secondary consumers Secondary and primary consumers Primary consumers Producers (plants) Figure 20.18 Species Diversity in Communities • Species diversity of a community consists of – Species richness, the number of different species in the community – Relative abundance of the different species, the proportional representation of a species in a community © 2010 Pearson Education, Inc. Woodland A Woodland B Figure 20.19 80 Key Relative abundance of tree species (%) Woodland A 60 Woodland B 40 20 0 Tree species Figure 20.20 • A keystone species is a species whose impact on its community is much larger than its total mass or abundance indicates. • Experiments in the 1960s demonstrated that a sea star functioned as a keystone species in intertidal zones of the Washington coast. © 2010 Pearson Education, Inc. Figure 20.21 Disturbances in Communities • Disturbances are episodes that damage biological communities, at least temporarily, by – Destroying organisms – Altering the availability of resources such as mineral nutrients and water. • Examples of disturbances are storms, fires, floods, and droughts • Disturbances may cause – The emergence of a previously unknown disease – Opportunities for other organisms to grow © 2010 Pearson Education, Inc. Figure 20.22 • Remember an ecosystem is all biotic and abiotic factors in an area. • A simple terrarium is a microcosm that exhibits the two major processes that sustain all ecosystems: – Energy flow, the passage of energy through the components of the ecosystem – Chemical cycling, the use and reuse of chemical elements such as carbon and nitrogen within the ecosystem © 2010 Pearson Education, Inc. al Energy flow Light energy Bacteria, protists, and fungi Chemical energy Heat energy Chemical elements Figure 20.25 • Energy flows through ecosystems. • Chemicals are recycled within and between ecosystems. • All organisms require energy for – Growth – Maintenance – Reproduction – In many species, locomotion • Each day, the Earth receives about 1019 kcal of solar energy, the energy equivalent of about 100 million atomic bombs. • About 1% is converted to chemical energy by photosynthesis. © 2010 Pearson Education, Inc. Open ocean Estuary Algal beds and coral reefs Desert and semidesert scrub Tundra Temperate grassland Cultivated land Northern coniferous forest (taiga) Savanna Temperate broadleaf forest Tropical rain forest 0 500 1,000 1,500 2,000 2,500 Average primary productivity (g/m2/yr) Figure 20.26 Ecological Pyramids • When energy flows as organic matter through the trophic levels of an ecosystem, much of it is lost at each link in the food chain. • Consider the example of a caterpillar. © 2010 Pearson Education, Inc. Plant material eaten by caterpillar 100 kilocalories (kcal) 35 kcal 50 kcal Cellular respiration Feces 15 kcal Growth Figure 20.27 • A pyramid of production illustrates the cumulative loss of energy with each transfer in a food chain. • The energy level available to the next higher level – Ranges from 5–20% – Is illustrated here as 10% © 2010 Pearson Education, Inc. Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers Producers 1,000 kcal 10,000 kcal 1,000,000 kcal of sunlight Figure 20.28 • The energy available to top-level consumers is small compared to the energy available to lower-level consumers. • This explains why – Top-level consumers require more geographic area – Most food chains are limited to three to five levels • The dynamics of energy flow apply to the human population, when humans eat – Plants, we are primary consumers – Beef or other meat from herbivores, we are secondary consumers – Fish like trout or salmon, we are tertiary consumers © 2010 Pearson Education, Inc. • The two energy pyramids that follow compare the amount of food available to humans if we are strictly either: – Vegetarians or – Carnivores • Eating meat of any kind is expensive economically and environmentally. © 2010 Pearson Education, Inc. Trophic level Human meat-eaters Secondary consumers Primary consumers Producers Human vegetarians Corn Cattle Corn Figure 20.29 Chemical Cycling in Ecosystems • Life depends on the recycling of chemicals. – Nutrients are acquired and waste products are released by living organisms. – At death, decomposers return the complex molecules of an organism to the environment. – The pool of inorganic nutrients is used by plants and other producers to build new organic matter. © 2010 Pearson Education, Inc. Figure 20.30 The General Scheme of Chemical Cycling • Biogeochemical cycles involve – Biotic components – Abiotic components from an abiotic reservoir where a chemical accumulates or is stockpiled outside of living organisms • Biogeochemical cycles can be local or global • Three important biogeochemical cycles are – Carbon – Phosphorus – Nitrogen © 2010 Pearson Education, Inc. The Carbon Cycle • The cycling of carbon between the biotic and abiotic worlds is accomplished mainly by the reciprocal metabolic processes of – Photosynthesis – Cellular respiration © 2010 Pearson Education, Inc. CO2 in atmosphere Burning Photosynthesis Cellular respiration Higher-level consumers Plants, algae, cyanobacteria Primary consumers Wood and fossil fuels Decomposition Wastes; death Decomposers (soil microbes) Plant litter; death Detritus Figure 20.32 The Phosphorus Cycle • Organisms require phosphorus as an ingredient of – Nucleic acids – Phospholipids – ATP • Phosphorus is also required as a mineral component of vertebrate bones and teeth. • The phosphorus cycle does not have an atmospheric component. © 2010 Pearson Education, Inc. Uplifting of rock Weathering of rock Runoff Phosphates in rock Animals Plants Assimilation Phosphates in solution Rock Solid phosphates Phosphates in soil (inorganic) Decomposition Detritus Decomposers in soil Figure 20.33 The Nitrogen Cycle • Nitrogen is – An ingredient of proteins and nucleic acids – Essential to the structure and functioning of all organisms • Nitrogen has two abiotic reservoirs: – The atmosphere – The soil • The process of nitrogen fixation converts gaseous N2 to ammonia and nitrates, which can be used by plants. • Most of the nitrogen available in natural ecosystems comes from biological fixation performed by two types of nitrogen-fixing bacteria. © 2010 Pearson Education, Inc. Nitrogen (N2) in atmosphere Assimilation by plants Plant Animal Organic compounds Organic compounds Death; wastes Nitrogen fixation Denitrifying bacteria Nitrates In soil (NO3–) Nitrogen-fixing bacteria in root nodules Detritus Decomposers Nitrifying bacteria Free-living nitrogen-fixing bacteria Decomposition Nitrogen fixation Ammonium (NH4+) in soil Figure 20.34 Nutrient Pollution • The growth of algae and cyanobacteria in aquatic ecosystems is limited by low nutrient levels, especially of phosphorus and nitrogen. • Nutrient pollution occurs when human activities add excess amounts of these chemicals to aquatic ecosystems. © 2010 Pearson Education, Inc. Figure 20.35 • Nitrogen runoff from Midwestern farm fields has been linked to an annual summer dead zone in the Gulf of Mexico. © 2010 Pearson Education, Inc. Mississippi River Light blue lines represent rivers draining into the Mississippi River (shown in dark blue) Summer Winter Figure 20.36 CONSERVATION AND RESTORATION BIOLOGY • Ecologists have discovered many environmental problems caused by human enterprises. • Ecological research is the foundation for – Finding solutions to these problems – Reversing the negative consequences of ecosystem alteration © 2010 Pearson Education, Inc. Biodiversity “Hot Spots” • Conservation efforts are often focused on biodiversity hot spots, relatively small areas that have – A large number of endangered and threatened species – An exceptional concentration of endemic species, those that are found nowhere else © 2010 Pearson Education, Inc. Equator Figure 20.37 • A movement corridor – Is a narrow strip or series of small clumps of suitable habitat – Connects otherwise isolated patches • Corridors – Can promote dispersal and help sustain populations – Are especially important to species that migrate between different habitats seasonally © 2010 Pearson Education, Inc. Figure 20.39 Restoring Ecosystems • Bioremediation uses living organisms to detoxify polluted ecosystems. • Researchers are investigating the use of plants to remove toxic substances from contaminated soil. © 2010 Pearson Education, Inc. Figure 20.41 The Goal of Sustainable Development • As the world population grows and becomes more affluent, the demand increases for the provisioning services of ecosystems, such as – Food – Wood – Water • Sustainable development aims to – Conserve biodiversity – Improve the human condition © 2010 Pearson Education, Inc. Figure 20.44